YAMA : (Ahimsa, Satya, Asteya, Brahmacharya, Apaigraha) : moral code

NYAMA : (Shaucha, Santosha, Tapas, Swadyaya,
Iswarapranidhana) : self purification, observances, study

ASANA : postures

PRANAYAMA : extension (control) of the breath

PRATYAHARA : sense withdraw

DHARANA : concentration

DHYANA : meditation

SAMADHI : realization, contemplation, absorption
(see YOGA MALA, Sri K. Pattabhi Jois)

The first four levels are external, the other four internal. Performing Asana, the practise of Yama and Nyama is possible and is a preparation for the next step of Pranayama.

The other four (internal) are more difficult and require constant practise for gradual development.